I think it is no secret now, when I tell you that the world is running out of oil. (See Hubbert's peak.) Up until now, most of our oil has been used to make energy (or as fuels). This has got to stop because the day is coming when oil will be more valuable than energy, and will be needed for other uses. (Should I mention global warming?) That brings up a new and timely idea.
If we think of using oil to make energy as a reaction:
Oil --> energy.
We should remind ourselves that the reaction is reversible, at least in principle:
Energy --> oil
There is an inefficiency involved in going either way. The existence of this reversible reaction has the effect of placing a link between the cost of energy and the cost of oil. Some examples:
1) The cost of oil can not be substantially lower than the cost of equivalent energy from other sources (allowing for inefficiency), otherwise energy production will shift to use of more oil. (Which just supposes that economics has more sway than common sense.)
2) The cost of oil can not be substantially higher than the cost of equivalent energy from other sources (allowing for inefficiency), in the long run, because man's inventiveness will allow oil to be made from energy.
The question then follows as to whether there are or can be practical means for making oil from energy.
We may say that we live in an exciting time, when the world has to face a transition from the "industrial age" when we have powered everything with fossil fuels. The daily advance of news on this, this summer, is quite surprising. The underlying question is, what will replace oil? Wind turbines, etc., make electricity, not oil. The question hasn't been very important until now, when we can see that we really are going to run out. There are maybe three answers to the question--
1) Biomass to oil, fuel, etc. An example is NREL's research on using the Fischer-Tropsch (or F-T) process to convert trash to oil--not the best approach. The direct conversion with pressure and heat is better (sorry, don't have the reference, now in pilot plant operation). There are many others, including my favorites: growing biomass at sea for conversion to methane, and producing "biodiesel" from low-value crop materials.
2) The darling of industry, converting coal (or natural gas, oil shale, etc.) to liquid fuels. This is already in use in one two-step process: "coal gasification" to synthesis gas, then coversion to long-chain hydrocarbons with the F-T process. This produces a very good-quality diesel fuel, or about anything else you want. Pretty rough on the environment, so only half a solution.
3) Efficient conversion of electricity or other high-quality energy directly to hydrocarbons. Most of the good alternate energy approaches produce electricity. Okay, I will list the best of these: wind, tide /wave, PV, and solar-thermal. A unique exception, a dish solar concentrator, can also produce high-quality heat (10,000 suns) at the focus.
Number three is exactly what I was talking about. It is the only one that makes sense but doesn't rely on photosynthesis. Notice that I have excluded hydrogen from consideration, as a replacement for oil and other liquid fuels. I know further that hydrogen can be made from electricity, and in turn can be used to make hydrocarbons, by the F-T process. This looks way too expensive and inefficient to get very far, in my judgement.
I was searching around on the internet last night, looking for new ideas on making synthetic oil or hydrocarbons--Ideas that would fall within #3. I found nothing! This topic, producing hydrocarbons from electricity or heat directly, is of great importance for the future of man. Though it may be a little early yet, this will be a major problem soon. When we (the world) turn our attention to it, solutions will quickly emerge. I see two paths:
1) Use of heat. Two reactions at high temperature have been mentioned in the past:
H2O --> HO + H --> H2 + O2
CO2 --> CO + O --> CO + O2
Removing the oxygen, the products together are "synthesis gas," which can be used to make alcohols or long-chain hydrocarbons by the F-T process. Or, either of the gases singly, with water or CO2, can be used to the same end.
There are surely many other known processes that I am unaware of.
2) Use of electricity to make hydrocarbons directly. This seems to be a largely unexplored field, having been at an economic disadvantage for the last century. Here, two approaches come to mind: plasma chemistry, driven by electrical power. A subset of this are the thermal processes mentioned in 1).
A second approach is well known, but not worked on currently, I think-- that is organic electrochemistry for making fuels. In principle, electrochemical reactions carried out in cells can make hydrocarbons and other organic materials. A few industrial processes already exist that do this sort of thing.
Michael Faraday reported an experiment that should be a point of beginning for research. He passed an electric current through a solution containing carbonate ion, and discovered that organic compounds were formed. (Formic acid or formaldehyde?)
I hope I have shed some warm light on Hubbert's peak.